1. Field of the Invention
The present invention relates generally to sheet or web material handling devices and, more particularly, to a web and sheet guide having a centering mechanism for centering a rigid sheet or web strip of stock material relative to a processing apparatus downstream of the guide.
2. Discussion of the Prior Art
When feeding stock material to a strip processing device, such as a die set or machine, it is essential that the center line or central axis of the strip of stock material be aligned with the central axis of the die as the stock material enters the die in order to ensure that the strip is properly formed in the device. However, strip material typically used in such processing operations frequently is not perfectly straight, but rather includes a camber or uneven width along its length. This camber or uneven width in the strip is sometimes caused by cutting wheels which may wear unevenly, thus causing deformation of the material being cut due to forces exerted on the strip during cutting. Such camber in a strip is amplified when the strip is later rolled into a web.
To obviate the problems created by such camber or uneven widths along the length of strips, it is conventional to arrange a trimming device at the inlet end of the processing device and to trim the edges of a strip passing into the device to provide a center line of the strip collinear with the central axis of the desired strip travel path through the device.
Further, by guiding the strip of material into the trimming device with one edge of the strip properly aligned with a side margin of the trimming device, it is possible to reduce the amount of trimming carried out on the strip by trimming only the one unaligned edge of the strip. Thus, it is possible to save material while preserving the alignment of the strip material entering the processing device.
An example of a guide assembly capable of use in guiding a strip of material either into a trimming device or directly into a die set, is illustrated in U.S. Pat. No. 2,726,859. In the patented device, a guiding mechanism is shown as including a pair of biased rollers which bias the stock material against a backing rail aligned with the side margin of the die machine. During feeding of strip material into the die or machine, the strip is urged against the rail so that the edge of the strip in contact with the rail is aligned with the side margin of the die or machine.
Although this type of construction is useful when the strip is being fed into a trimming device prior to passing into a die set, several problems arise when the construction is employed directly in front of the die set. For example, because the guide assembly aligns an edge of the strip with a side margin of the die set rather than aligning the central axis of the strip with the central axis of the die set, the central axis of the strip may be displaced from the central axis of the die set as variations in the width of the strip occur. Thus, proper machining of the strip, which depends upon proper orientation of the centerline of the strip, is adversely affected.
In order to avoid improper alignment of a strip as it is fed into a processing machine, it has been attempted to provide an apparatus which will align the central axis of the strip with the central axis of the feed path entering the processing machine. In U.S. Pat. No. 1,440,385, a guide mechanism is illustrated in which a plurality of independently mounted and biased rollers are provided on a plate and engage the edges of the strip to position the strip for travel along a desired path.
However, numerous drawbacks exist in a construction of this type. For example, because of the large number of parts employed in such constructions, many very precise machining operations are necessary in order to provide proper cooperation between the interconnected elements. In addition, several springs are required in the apparatus which may exert uneven biasing forces on the rollers so as to cause misalignment of the rollers during a guiding operation.